The reason for this is that there are replication tables included in the database that was backed up. If you look at the tables, you'll see them. This causes Sql Server to recognize the fact that they were part of replication. However, when it is restored to another server, the other supporting tables in the MSDB are not there, hence the in-ability to delete the publications. This is a common issue with backing up replicated databases, and restoring to another server.
You have two options.
1. Clean up the system replication tables manually by deleting them in the database restored.
2. Shutting down and deleting the publications prior to backing up.